This invention relates to an optical scanning apparatus and method.
Conventionally, a multi-beam optical scanning system capable of scanning plural lines at a time is proposed as a high speed processing means for use in an output apparatus of a computer, of an information receiving and recording apparatus for facsimile systems, or of copying machines.
One example of such multi-beam optical scanning systems is the so-called laser plotter utilizing laser beams, in which a laser plotter utilizing a rotary polyhedral mirror is used as an optical scanning means.
Referring to FIG. 1, there is shown a conventional laser recording apparatus. In FIG. 1, reference numeral 1 represents a laser light source, reference numeral 2 a beam expander, reference numeral 3 a convergent lens, reference numeral 4 an acousto-optic device driven by multi-frequency, reference numeral 5 a magnification adjustment lens, reference numeral 6 a cylindrical lens, reference numeral 7 a rotary polyhedral mirror, reference numeral 8 a lens, reference numeral 9 another cylindrical lens, and reference numeral 10 a photoconductor drum.
A laser beam L.sub.b coming from the laser light source 1 is expanded in its beam diameter by the beam expander 2 and is then caused to converge by the convergent lens 3 and illuminates the acousto-optic device 4.
In the meantime, modulated signals, which are modulated by plural image signals, are applied to the acousto-optic device 4 (arrow 4a) and therefore plural beams containing each image information, such as L.sub.b1, L.sub.b2 and L.sub.b3 in FIG. 1 are projected from the acousto-optic device 4.
These beams L.sub.b1, L.sub.b2 and L.sub.b3, passing through the magnification adjustment lens 5 and the cylindrical lens 6, are continuously reflected by the rotary polyhedral mirror 7, which is rotated by a motor (not shown) and pass through the lens 8 and the cylindrical lens 9 and reach the surface of the photoconductor drum 10 to be scanned, scanning the surface.
Thus, in the conventional technique, rotary polyhedral mirrors and galvanomirrors are employed as the optical scanning means. However, the polyhedral mirrors and galvanomirrors are expensive since an extremely high accuracy is required to manufacture them. Therefore, it is difficult to provide recording apparatus employing such polyhedral mirror or golvanomirror at a low cost on the market.